In complex rotating machines, such as gas turbine engines, it is often desirable or necessary to send data across rotating interfaces. For example, in a turboprop engine, measurement data from an instrumentation package on a rotating propeller hub may need to be sent to a central processor or memory device mounted on the static engine casing. Likewise, command data may need to be sent from a command unit mounted on the static engine casing to drive actions (such as measurements) by devices on the propeller hub.
Although in principal it may be possible to transmit such data using radio techniques, in practice a physically closed transmission route may be desirable, for example to improve immunity from interference or because radio signals may interfere with engine or aircraft operation.
Thus conventional mechanisms for transferring data between rotating and static components use 360° devices such as slip rings or induction couplings that maintain continuous coupling, and hence a continuous communication channel, between the data transmitter and receiver.
The reliability and performance of such continuous couplings is generally improved by mounting the couplings close to the axis of rotation, where the relative velocity across the rotating interface is lower. Also, the weight and size of continuous couplings can be reduced by mounting close to the axis. Thus, for example, in gas turbine engines it might be desirable to mount a continuous coupling surrounding a drive shaft. However, it is often not practical to mount such a coupling close to the axis of rotation, e.g. due to a lack of easy access to the centre of the engine which can compromise reliability and/or maintainability.